1. Field of the Invention
This invention relates to a gas flow valve and a sphygmomanometer using such a gas flow valve.
2. Description of the Prior Art
A conventional gas flow valve of this type has been disclosed in the specification of Japanese Utility Model Application Laid-Open (KOKAI) No. 61-142003 filed by the present applicant. This gas valve flow will be described with reference to the drawings.
FIG. 13 is an external view of a flapper used in the prior-art gas flow valve of the present applicant, FIG. 14 is a plan view illustrating the main body of the prior-art gas flow valve the center of which is shown broken away, and FIG. 15 is a view showing the right side of FIG. 14.
As shown in FIG. 13, the flapper 30 has a generally T-shaped external form and is fabricated by machining a thin sheet. The flapper 30 is used mainly as a body for regulating the amount of leakage of gas flowing through the valve. Here the thin sheet constituting the flapper 30 is a thin piece of plastic or the like, the base end of which has a vane 30a projecting to the left and right at right angles to the longitudinal direction of the flapper 30.
As illustrated in FIG. 14, each vane 30a has a shape and dimensions that enable the vane 30a to fit into a groove 34 formed in a main body 32 of the gas flow valve. The longitudinal dimension of the flapper 30 is such that when the vane 30a is fitted in the groove 34 of main body 32, the distal end of the flapper 30 will pass through a linear opening or slit 38 provided in one end of the main body 32.
When the flapper 30 is received in an air passage 36 of the main body 32, as shown in FIG. 14, the slit 38 is opened so that gaps 40 are formed on both sides of the flapper 30. As a result, venting takes place through the gaps 40.
However, if the portion of the flapper 30 contacted and held by the slit 38 is made large in size in order to form the gaps 40 on both sides of the flapper 30 in this air flow valve using the conventional flapper, a variance in the shape of the slit 38 from one valve to another, which is ascribable to differences in the material forming the main body 32, has a greater effect, and therefore the performance of the air flow valve will also differ from one valve to another.
Furthermore, since the flapper 30 is not fixed sufficiently with respect to the main body 32, the flapper moves from side to side at the slit 38. Consequently, the velocity of gas flow is not consistent.